The Great Medical Encyclopedia (Russia) indicates that screening (from the English. Screening — sifting) is a methodological approach used, in particular, in medicine for mass examination of the population (its individual contingents) in order to identify a specific disease (group of diseases) or factors contributing to the development of this disease (risk factors).

The UK National Screening Committee defines screening as the process of identifying risk factors for a disease or disease that is not yet clinically apparent.

Screening is an indicative sorting process. Visually, the screening process can be illustrated as a sieve designed to separate individuals suspected of having a disease from those presumed not to have it. A screening test is never 100% accurate; it does not give certainty, but only indicates the likelihood of the risk of having the desired disease (or its absence).

The purpose of screening is to identify individuals in an apparently healthy population at higher risk for a disease or condition in order to suggest earlier treatment or intervention, which in turn will improve the health status of some of those screened.

Screening and early diagnosis are different concepts. Screening offers testing of asymptomatic populations, while early diagnosis is intended to detect pathological conditions as early as possible in patients with already present symptoms.

The goals of screening programs include:

• reducing mortality through early detection and early treatment of the disease;
• reducing the incidence of the disease by identifying and treating pre-morbid conditions;
• reducing disease severity by identifying individuals with the disease in question and suggesting effective treatment;
• expanding choice by identifying diseases or risk factors earlier in life when more treatment options are available.

The goals of screening programs should be set out in a population screening policy, documented in law or in an official regulation, decision or directive.

Screening types:

1. By population coverage:

• National/regional population-based screening programs for risk factors or specific diseases. The population in these programs are populations of a certain age and gender without a history or current clinical case of CVD for which the patient is receiving treatment.
• Screening programs for a target/sample group (for example, with risk factors for a specific disease, conducted for research purposes as a pilot assessment of the effectiveness of screening for certain diseases, or “commercial screening” programs offered by medical centers, insurance organizations, etc.).

2. According to the mechanism of inclusion in screening:

Voluntary screening:

• Screening Invitation – A targeted invitation to individuals who are eligible to be tested for a specific disease in accordance with a national/regional screening program.
• Independent application for screening when creating at the national or regional level the possibility of passing it and obtaining information about the possibility of passing screening through the media, including specialized Internet sites.
• Opportunistic screening — involves conducting various tests (studies) to identify a disease or risk factors when a person seeks any medical help or specialist advice.
• “Involuntary screening” is a mandatory medical examination conducted at the request of the employer before the candidate is hired.

Laboratory research:

Laboratory studies during screening are divided into routine and special.

Routine studies allow you not to «miss» the most common deviations in the body. These include:

• general blood analysis; • general urine analysis; • biochemical blood tests — total protein, liver tests, creatinine/urea, blood glucose; • analysis of feces for occult blood.

Special screening studies are aimed at finding diseases and conditions in the risk zone for which the patient is located. Among them, the most common and important are:

• cholesterol and its fractions — to assess the risk of atherosclerosis;
  • glycated hemoglobin (HbA1c) + HOMA index (designed to determine insulin resistance in the ratio of glucose and insulin levels) — to assess the development of prediabetes, impaired glucose tolerance and insulin resistance; • TSH — to exclude the involvement of the thyroid gland in the «masked» symptoms; • HbsAg — to eliminate the «masks» of hepatitis B; • cortisol — the «stress hormone» — it is especially important to assess the chronic increase in this hormone; • prostate specific antigen (PSA, PSA) in men, since its high level in the blood serum gives grounds to suspect the presence of prostate cancer; • PAP test and HPV (human papillomavirus) — to rule out the risk of developing cervical cancer.

Instrumental screening:

Instrumental screening includes:

• ultrasonography;
• electrocardiography;
• electroencephalography;

radiography and others.

Output:

Screening is the presumptive identification of an undetected disease or defect through the use of tests, tests, or other procedures that can be applied quickly. Screening tests make it possible to distinguish apparently healthy individuals who are presumed to suffer from certain diseases from those who presumably do not have these diseases. Screening tests do not claim diagnostic value. Individuals with positive or suspicious results should be referred to physicians for diagnosis and appropriate treatment.